Due to alarming increase in population and rapid industrialization, drinking water quality is being deteriorated day by day in Pakistan. This review sums up the outcomes of various research studies conducted for drinking water quality status of different areas of Pakistan by taking into account the physicochemical properties of drinking water as well as the presence of various pathogenic microorganisms. About 20% of the whole population of Pakistan has access to safe drinking water. The remaining 80% of population is forced to use unsafe drinking water due to the scarcity of safe and healthy drinking water sources. The primary source of contamination is sewerage (fecal) which is extensively discharged into drinking water system supplies. Secondary source of pollution is the disposal of toxic chemicals from industrial effluents, pesticides, and fertilizers from agriculture sources into the water bodies. Anthropogenic activities cause waterborne diseases that constitute about 80% of all diseases and are responsible for 33% of deaths. This review highlights the drinking water quality, contamination sources, sanitation situation, and effects of unsafe drinking water on humans. There is immediate need to take protective measures and treatment technologies to overcome unhygienic condition of drinking water supplies in different areas of Pakistan.
Pakistanis are situated in southern Asia, bordering with India in the east, Afghanistan in the west, and China in the north. In the east of Pakistan, there exist mountains of Himalaya and Karakorum. In the north, Hindukush ranges exist, and hill regions (up to 4700 m) in the northwest and in the upland Baluchistan plateau exist. The climatic conditions are mostly arid to semiarid with varying levels of average rainfalls in different areas of Pakistan [
Pakistan has been blessed by nature with enough surface and groundwater resources. Industrialization, urbanization, and rapid population growth have placed huge stress on water resources [
In most of the cities of Pakistan, the elementary source of provision is ground water supply, which contains various pathogens including many viral, bacterial, and protozoan agents causing 2.5 million deaths from endemic diarrheal disease each year [
Water pollution is a physical process that occurs in various water resources such as lakes, ground water, and rivers due to anthropogenic activities [
When water comes from surface water resources, it is necessary to make it safe for drinking purposes. Chlorination is the popular method for disinfection of drinking water at treatment plant and in sanitation system [
Drinking water should be free from color, turbidity, odor, and microbes. It should be esthetically pleasant. Due to increasing population of Faisalabad, contaminated water is the most alarming problem. In 1999, Faisalabad required about 64.7 million gallons of drinking water supply daily to fulfill needs. But unfortunately 3 million gallons of this water came from domestic pumps that come out from subsoil water and tube well [
The current water supply is about 79% in Pakistan [
Human health is adversely affected by various agents like pathogens, bacteria, various minerals, and organic substances that are present in unsafe drinking water. A significant proportion of population in developing countries is suffering from health-related issues due to unsafe drinking water and microbial contamination [
In Pakistan, approaches to safe drinking water have reached acceptable limits. Reference [
In Pakistan, the main reasons of waterborne diseases in drinking water are the addition of municipal sewage and industrial wastewater at different points of the water distribution network as well as lack of water disinfection and water quality monitoring at treatment plants. Pakistan National Conservation Strategy [
In Pakistan, water quality in most of the cities is decreasing quickly. The major cause of decreasing water quality is the ground water supply. According to [
Nature has gifted Pakistan with enough ground and surface water resources. Unfortunately anthropogenic activities such as industrialization, increase in population, and improper utilization decrease the quantity and damage the quality. According to Jamshed Iqbal Cheema (Chairman: Pakistan Agriculture Scientists Association), the per capita water availability in Pakistan at the time of independence was 5,600 cubic meters [
Per capita water availability decreasing tremendously in Pakistan.
In Punjab, 7% of all the rural population depends on dug wells and rivers for water supply. It seems that Punjab has best water supply system among all the provinces. This ratio is 24% in Sindh and people are utilizing water from unprotected sources. The rural communities of Khyber Pakhtunkhwa (KP) and Baluchistan using water from surface and dug well are about 46% and 72%, respectively, [
Dependence of water supply in the provinces of Pakistan.
Water for drinking purposes mainly comes out from the surface and underground aquifers near the rivers or canals. The surface water quality is dropping rapidly due to the addition of raw municipal and industrial effluents and agriculture runoff into water resources [
About 70% of water for drinking purposes comes from aquifers [
Water pollution is the deterioration of water quality due to the addition of wastes coming from industries, domestic and agriculture. Utilization of such water for beneficial use causes contrary effects on environment and public health. Industrialization and emergence of urban units placed immense stress on water resources and discharge of wastewater into natural water resources that decreases ground and surface water quality [
The most serious pollutants in terms of human health worldwide are pathogenic organisms. Altogether, at least 25 million deaths each year occur due to these water-related diseases, including nearly two-thirds of the deaths of children under five years of age. The main and major source of biological agents is unprocessed and unconventional treatment of human waste [
The physical, biological, and chemical properties of drinking water have great importance because a minor fluctuation in these parameters affects the human health. The pH is crucial factor that greatly affects water quality and quantity of pollution in water bodies [
National Standards for Drinking Water Quality.
Parameters | Standard values for Pakistan | WHO standards |
---|---|---|
Biological | ||
|
||
All water intended for drinking ( |
Must not be detectable in any 100 mL sample | Must not be detectable in any 100 mL sample |
Treated water entering the distribution system ( |
Must not be detectable in any 100 mL sample | Must not be detectable in any 100 mL sample |
Treated water in the distribution system ( |
Must not be detectable in any 100 mL sample |
Must not be detectable in any 100 mL sample |
|
||
Physical | ||
|
||
Color | ≤15 TCU | ≤15 TCU |
Taste | None | None |
Odor | None | None |
Turbidity | <5 NTU | <5 NTU |
Total hardness as CaCO3 | <500 mg/L | — |
TDS | <1000 | <1000 |
pH | 6.5–8.5 | 6.5–8.5 |
|
||
Chemical | ||
|
||
Essential inorganic | mg/L | mg/L |
|
||
Aluminum (Al) mg/L | ≤0.2 | 0.2 |
Antimony (Sb) | ≤0.005 (P) | 0.02 |
|
||
Arsenic (As) | ≤0.05 (P) | 0.01 |
Barium (Ba) | 0.7 | 0.7 |
Boron (B) | 0.3 | 0.3 |
Cadmium (Cd) | 0.01 | 0.003 |
Chloride (Cl) | <250 | 250 |
Chromium (Cr) | ≤0.05 | 0.05 |
Copper (Cu) | 2 | 2 |
|
||
Toxic inorganic | mg/L | mg/L |
|
||
Cyanide (CN) | ≤0.05 | 0.07 |
Fluoride (F) |
≤1.5 | 1.5 |
Lead (Pb) | ≤0.05 | 0.01 |
Manganese (Mn) | ≤0.5 | 0.5 |
Mercury (Hg) | ≤0.001 | 0.001 |
Nickel (Ni) | ≤0.02 | 0.02 |
Nitrate (NO3) |
≤50 | 50 |
Nitrite (NO2) |
≤3 (P) | 3 |
Selenium (Se) | 0.01 (P) | 0.01 |
Residual chlorine | 0.2–0.5 at consumer end, 0.5–1.5 at source | — |
Zinc (Zn) | 5.0 | 3 |
|
||
Organic | ||
|
||
Phenolic compounds (phenols) mg/L | ≤0.002 | |
Polyaromatic hydrocarbons (PAH) g/L | 0.01 (by GC/MS method) |
In Pakistan, microbial pollution has been discovered as one of the serious problems in rural as well as urban areas. This is due to the leakage of pipe, pollution from sewage lines intrusion into drinking water supplies, and so forth.
Chemical contaminants come from industries, soil sediments, and runoff from agriculture, that is, pesticides and fertilizers, and enter into water resources. In Pakistan, the application of fertilizer and pesticides is, respectively, about 5.6 million tons and 70 thousand tons according to Gross Operating Profit (GOP) figures. These chemicals, commonly insecticides, leach into ground water resources by mixing with irrigated and rain water. During 1988–2000, about 107 samples were collected from ground water and 31 samples indicated pesticide contamination that was clearly beyond the Food and Agriculture Organization (FAO) and WHO permissible limits. In Pakistan, another important trouble with ground water is highest concentration of salts, which is mainly due to irrigation, soil salts dissolution, sea water encroachment, and chemical industries. Salinity impacts the major areas of Baluchistan, KP, and Punjab. Effluent from industries and domestics contains high concentration of arsenic that is becoming a severe problem. In major cities of Sindh and Punjab, about sixteen percent of people are exposed to more than 50 ppm of arsenic. Higher concentration of fluoride above permissible limits causes a trouble in major areas of Baluchistan, Punjab, and Sindh. The dental fluorosis diseases are commonly found in Sindh, Punjab, and KP.
In Pakistan, floods have been creating great environmental problems. They damage drains and ultimately cause spillage of sewage water into water bodies. Severe flooding destroys buildings and standing crops. All these may cause release of toxic chemicals and oil into river, streams, and lakes, and so forth and may lead to death of aquatic life. A lot of chemical contaminants mix with flood water on its way. The current severe flood (2010) and heavy rains damaged 80% of Nowshera, devastating 40% of infrastructure. The total destroyed and damaged houses were in the range of 10,000 and 40,000, respectively [
To evaluate the drinking water quality of Islamabad, drinking water samples had been collected from schools and colleges. Analysis showed that 20 samples out of 30 were contaminated with fecal microbes and not fit for drinking purposes [
Geographic Information System and Water Quality Index study of bore wells and open wells of Rawalpindi and Islamabad revealed that more than half of samples were poor in quality for drinking due to overexploitation of groundwater resource, agricultural impact, and direct release of contaminants [
Drinking water contamination with
Physicochemical parameters on water quality of Islamabad indicated that alkalinity, hardness, and total dissolved solids in all samples were within safe limits as recommended by Pakistan Standard and Quality Control Authority (PSQCA). But coliform and
Physicochemical and biological parameters of drinking water quality of twin cities.
Islamabad and Rawalpindi | Total | Percentage of samples contaminated | References | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
pH | EC | TDS | Turbidity | Hardness | Physicochemical |
Total coliform | Fecal coliform |
|
Bacteriological values | |||
Islamabad (Isd.) | 271 | — | — | — | — | — | 10.3 | — | — | — | 77 | [ |
CDA (Isd.) | 196 | — | — | — | — | — | 3.6 | — | — | — | 5.1 | [ |
F-10, G-6, G-10, H-9, I-9, Dhok Kala khan, commercial market, New Mirpur, Pindora, Dhoke Ratta | 10 |
— | — | 4 |
— | 4 |
— | Present | Present | Present | — | [ |
Islamabad & Rawalpindi | 22 | — | — | — | — | — | 46 | — | — | — | — | [ |
Islamabad & Rawalpindi | 130 | — | — | — | — | — | — | Present | Present | Present | — | [ |
Islamabad | 55 | — | — | — | — | — | 14.5 | Present | Present | Present | — | [ |
Islamabad | 32 | — | — | — | — | — | — | Present | Present | Present | — | [ |
Drinking water quality and chlorination effect of two villages in south Punjab were analyzed [
Faisalabad is known as polluted industrial city due to the inadequate treatment facilities. The impact on water resources near Samundri drain in Faisalabad showed that the ground water quality was the worst as 90% of samples were above the WHO limits with respect to TDS, Na, K, Cl, and SO4 [
The physicochemical analysis of drinking water was carried out to evaluate drinking water quality of Faisalabad city. The turbidity, hardness, pH, and TDS were found within safe limits of WHO guidelines. The microbial analysis showed that all samples were contaminated with total coliforms and
Chemical and biological analyses of drinking water samples collected from three different sites in Faisalabad showed that pH was found within the range according to WHO standards and electrical conductivity was found above the permissible limits. Higher electrical conductivity (EC) is due to the dissolution of subsoil minerals and leaching into ground water. Bacteria were also found in water samples which showed fecal contamination. All these analyses indicate that water is not fit for drinking purposes [
Water quality monitoring was carried out to access chlorination of supply lines in Cantonment area, Rawalpindi. The temperature of all samples was above the critical values as recommended by WHO. Water temperature is an important factor for microbial growth [
Drinking water quality of urban areas of southern Lahore was evaluated before and after monsoon season. It was seen that the values of pH of all sources and house connections were well within the WHO desirable limit both before and after the monsoon season. The turbidity in water was less than the desirable limit of 0.5 NTU while it was more than 0.5 NTU before and after the monsoon at two sites. The hardness at all the sources (T/W) and house connections was less than the WHO guideline. The TDS values were in critical limits. The bacteriological contamination was also not detected in water samples before and after monsoon. Fecal contamination showed that water had come in contact with human feces [
Drinking water quality test carried out in twelve districts of Punjab showed that microbial and heavy metal (arsenic) were major contamination found in all districts. At least 45% of the samples of Kasur district were found to be contaminated with microbes. About 73%, 100%, 64%, 94%, 100%, and 88% of drinking water samples of Sheikhupura, Lahore, Gujranwala, Multan, Kasur, and Bahawalpur were highly contaminated with arsenic. Total dissolved solids (TDS) were found above the permissible limits in Sargodha, Sheikhupura, Kasur, Faisalabad, and Rawalpindi [
The chemical analysis of groundwater samples collected from rural areas of Punjab indicated that water was unfit for drinking purpose. High values of EC,
The physicochemical analysis of different samples collected from urban areas of Faisalabad showed that the pH value and hardness were within range as recommended by WHO. The values of alkalinity, TDS, sulphate (SO4), and chlorides were found above the permissible limits of WHO. Overall the ground water used for drinking purpose in urban areas of Faisalabad was intensively polluted with sewerage water [
Physicochemical and biological parameters of drinking water quality of Punjab.
Punjab |
Total | Percentage of samples contaminated | References | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
pH | EC | TDS | Turbidity | Hardness | Physicochemical |
Total coliform | Fecal coliform |
|
Bacteriological values | |||
University of Punjab, Lahore | 18 | — | — | — | — | — | 11 | Present | — | — | 11 | [ |
Faisalabad | ||||||||||||
Bottled water | — | — | — | — | — | 10 | ||||||
Ground water | 54 | — | — | — | — | — | 50 | — | — | — | — | [ |
WASA supply lines | — | — | — | — | — | 20 | ||||||
Faisalabad | 54 | — | — | — | — | — | 90 | — | — | — | — | [ |
Faisalabad | 225 | — | — | — | — | — | — | Present | — | Present | 79 | [ |
Samundri, Faisalabad | 110 | — | — | — | — | — | — | Present | Present | Present | — | [ |
Water samples were collected from tube wells and storage tanks to determine the drinking water quality in rural areas of Peshawar. Results indicated that just 13% of the samples were negative for bacterial contamination, 40% were found in the satisfactory level, and 47% of the samples were found to be highly contaminated with
The drinking water samples collected for bacteriological detection demonstrated that about ninety-two percent of water samples were detected as contaminated [
The physical and chemical parameters of drinking water in Narangi and sounding areas of Swabi district demonstrated that the physical parameters were within permissible limits but regarding chemical parameters Pb and nitrite concentrations were found higher than WHO limits [
Water samples collected for physicochemical analysis from tehsil of Jamrud and Landikotal, Khyber agency, showed that all parameters were within range set by WHO. However, the concentration of Ca and Mg exceeds the limits of WHO. The heavy metal concentrations were also below the WHO permissible limits. But Cd concentration was higher than WHO permissible limits [
Chemical and microbial aspects of water samples collected from four cities, that is, Abbottabad, Mardan, Peshawar, and Manghora, were analyzed. More than 55% of all samples from these cities were highly contaminated with microbes. In KP, iron contamination was enlisted as second major contamination. In Peshawar and Mardan more than 38% and 67% of samples were contaminated with iron, respectively [
The microbial and physical investigation of drinking water quality in new urban Peshawar indicated that the pH was within permissible limits but the value of EC in five tube wells, seven supply channels, and nine storage tank samples was found above critical values. Similarly, the TSS values of water samples collected from supply channels, storage points, and tube wells were 30%, 60% and 10% beyond the critical limits of WHO. Bacteriological analysis showed that about one-third of all samples were not detected to have bacteriological contamination, while others were contaminated [
The water quality from different villages of Nagar valley revealed that all the tested parameters, that is, temperature, pH, turbidity, electrical conductivity, total dissolved solids, total coliform bacteria, total fecal bacteria, calcium hardness, cyanuric acid, and total alkalinity, were meeting the prescribed standards of WHO and EPA [
Physicochemical and biological parameters of drinking water quality of Khyber Pakhtunkhwa (KP).
Khyber Pakhtunkhwa |
Total | Percentage of samples contaminated | References | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
pH | EC | TDS | Turbidity | Hardness | Physicochemical |
Total coliform | Fecal coliform |
|
Bacteriological values | |||
Peshawar | 74 | — | — | — | — | — | Pb, Cd contamination | — | — | — | — | [ |
Khyber agency | 50 | — | — | — | — | — | Cd | — | — | — | — | [ |
New urban Peshawar | 30 | — | 100 | — | 90 | — | — | Present | Present | Present | — | [ |
Gilgit-Baltistan | 27 | — | — | — | — | — | — | Present | — | — | — | [ |
Biological and chemical water quality of Baluchistan are not satisfactory as revealed by various studies. In four cities of Baluchistan, that is, Ziarat, Loralai, Quetta, and Khuzdar, the water quality was badly contaminated with microorganisms making water unfit for human use. Water samples of these cities showed that NO3 concentration was higher than the recommended limits of WHO. About 50% of water samples, collected from Ziarat, were found highly contaminated with NO3 [
Temperature examination revealed a little fluctuation in results between 12.10 and 13.50°C. The highest value was determined in Thole channel water while the lowest was found in Nilt tank water. According to WHO and EPA, turbidity must not exceed 5 NTU and water having turbidity less than 1.00 NTU is excellent for domestic consumption. Turbidity of all samples was less than 5 NTU [
The bacteriological and physicochemical study of Hingol River situated at Hingol National Park was carried out, where the majority of its inhabitants are leading nomadic life style [
Physicochemical and biological parameters of drinking water quality of Baluchistan.
Baluchistan |
Total | Percentage of samples contaminated | References | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
pH | EC | TDS | Turbidity | Hardness | Physicochemical values | Total coliform | Fecal coliform |
|
Bacteriological values | |||
Hingol river, Baluchistan | 22 | — | 12.5 | — | — | — | — | Present | Present | — | — | [ |
Quetta | 200 | — | — | — | — | — | 39 | — | — | — | 60 | [ |
Khudar, Loralai, Quetta, and Ziarat | 66 | — | — | 6 | 7.5 | — | 57.5 | Present | Present | Present | 80.3 | [ |
Quetta | 16 | — | 12.5 | — | — | — | — | — | — | — | — | [ |
The drinking water quality of Khairpur, Sindh, showed high level coliform and fecal coliform contamination in drinking water at different points; therefore, it is not suitable for drinking purpose. It is evident from the results (high coliform and fecal coliform count at all 3 levels) that the quality of drinking water is further deteriorated in the distribution system which may be due to the leakage of pipes where sewage water enters into the municipal water. At the consumer level, the drinking water is getting more contaminated due to the unhygienic handling and uncovered storage tanks. Drinking water quality should have no coliform as well as fecal coliform present in 100 mL or 0 colony forming units (cfu) per 100 mL WHO [
The ground water of different villages in district Khairpur, Sindh, was analyzed physicochemically for drinking and irrigation purposes. The chemical and physical characteristics of all samples were above the WHO guidelines and water was not fit for drinking as well as for irrigation purposes [
Water shortage is a major issue in Karachi city, which is worse in slum areas having poor infrastructure and limited facilities. The physicochemical analysis of drinking water supply lines in Orangi Town, Karachi, showed that physicochemical characteristics were within WHO permissible limits except sulphates. The microbial investigation revealed that all samples were highly contaminated with total coliform, fecal coliform, and
Physicochemical and biological parameters of drinking water quality of Sindh.
Sindh |
Total | Percentage of samples contaminated | References | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
pH | EC | TDS | Turbidity | Hardness | Physicochemical values | Total coliform | Fecal coliform |
|
Bacteriological values | |||
Khairpur, Sindh | 68 | — | 50 | 20.5 | — | 13.11 | — | — | — | — | — | [ |
Orangi Town, Karachi | 46 | — | — | 100 | — | — | 39 | Present | Present | Present | 80.43 | [ |
Sindh | 35 | — | — | 50 | — | 21.88 | — | — | — | — | — | [ |
Sindh | 46 | — | — | — | 100 | — | — | Present | Present | — | — | [ |
Gulshan-e-Iqbal, Karachi | 12 | — | — | 8.3 | — | — | — | Present | Present | Present | 41.66 | [ |
Qualitative analysis of water resources that are used for drinking purposes showed that the physical parameters of three sampling sites such as bore well, dug well, and hand pumps were not according to the recommendations of PEPA and WHO [
Drinking water quality of the Sindh province is also poor as that of other provinces. About 67%–93% of samples collected from different locations in three main cities, that is, Sukkur, Hyderabad, and Karachi, showed that water is unsafe for drinking purposes due to microbial and chemical contamination [
The pH value of Keenjhar lake, located in Theta, Sindh, was within limits but color was brown to dark brown which is not acceptable for drinking purposes. The EC values of the samples were found to be above the WHO permissible limits.
Due to the poor sanitation system, treatment, and monitoring, drinking water quality deteriorates. The presence of toxic chemicals and bacteria in drinking water causes adverse effect on human health. Due to the fecal contamination, people have been suffering from waterborne diseases. In rural and urban areas of Pakistan, cases of waterborne diseases, typhoid, dysentery, cholera, and hepatitis are systematically reported. However, it is very difficult to properly quantify the danger due to several reasons. They include underreporting of diseases and poor record maintenance in healthcare centers and hospitals related to diseases caused by poor water quality [
Several studies have reported health-related problems due to poor drinking water quality. For example, the concentration of nitrate (NO3) was found above the permissible limits causing blue baby syndrome in bottle fed babies [
In Peshawar, most of water samples were found to be contaminated with coliform bacteria. In Rawalpindi, the gastroenteritis was reported in 2000; the contaminated water was the source. In Karachi, it was also found that the drinking water samples were heavily contaminated with total and fecal coliform. In Khairpur, a city of 0.12-million population, water quality seems to be poor and therefore could be a potential source for waterborne diseases especially among children.
In Islamabad and Rawalpindi, 4000 cases of hepatitis were registered and were due to unfit drinking water and improper treatment [
Unsafe drinking water is a major cause of the disease, which otherwise may be prevented, in particular in young children in developing countries. Pathogens present in drinking water including many viral, bacterial, and protozoan agents caused 2.5 million deaths from endemic diarrheal disease each year [
Management strategies should cover protection of sources from contamination, drinking water distribution lines upgradation and their proper maintenance, and monitoring and awareness of the people [
There is a poor framework for the legislation of drinking water supplies. Drinking water quality standards should be provisionally established for the treatment and maintenance of drinking water distribution system. Water and Sanitation Agency (WASA) should take action with the help of private institutions to protect water resources and control pollution from its source. A great attention is also required to stop the saline water intrusion into the fresh ground water resources.
Government should take action for the maintenance, proper functioning, and handling of already present drinking water treatment plants. There is a lack of proper sampling system of the drinking water treatment plants to ensure that water is safe and fit for drinking in urban areas of Pakistan. To stop the spread of waterborne diseases, there is need for proper functioning, inspection, and sampling analysis twice a year to ensure safe drinking water according to the quality standards.
Proper maintenance of water distribution system and chlorination should be done according to the law and regulations to kill pathogens. Government should provide the latest and reliable instruments and trained personals for the drinking water quality analysis.
In Pakistan, there are few industries that have their own water treatment plant to treat wastewater. Government should take strict action for their industrial effluent disposal according to the NEQS under the 1997 Act. If any industry is found to be violating the rules, it should be punished with heavy fine and imprisonment.
Public awareness campaigns should be started at school, college, university, and community level to address the significance of secure drinking water. NGOs might act in this facet. Rural communities should adopt safe control methods for protecting water storage in houses and simple disinfection technologies of drinking water.
A lot of studies show that boiled drinking water reduces risk of waterborne diseases [
This review documented the studies conducted in Pakistan on drinking water quality status and contamination, which accounted sewerage water (fecal) mixing with drinking water as dominant and primary contaminant due to the poor sanitation and sewerage system. Second source of contamination is chemical pollution from toxic substances from the industrial effluents, textile dyes, pesticides, nitrogenous fertilizers, arsenic, and other chemicals. There is a need to maintain and upgrade regular inspection of already present treatment plants. Nowadays, Government of Pakistan is going to install drinking water filter all over Pakistan. The results drew attention that sewerage contamination with drinking water must be considered as an important environmental and health issue.
All authors declare having no conflicts of interest regarding the publishing of this paper.
This study was funded by the National Natural Science Fund (Project no. 31501342) of China (2013AA102601).